The objective of this proposal is to determine the feasibility of developing an HTLV-I vaccine using methods which were successfully used in the feline leukemia virus system. The approach will be to use a HTLV infected cell product as the vaccine material. Tissue culture fluids from HTLV infected cells grown under appropriate conditions will be collected and concentrated. The concentrate will be tested for antigenicity, first in rabbits and then in subhuman primates. Antibody titers to HTLV-I will be measured in these animals and used as a criterion for determining the vaccine potency. Vaccination and challenge studies will be conducted in subhuman primates to determine immunoprophylaxis.